If you liked the Medaka Box manga, the Anime-Planet community thinks you'd like:
Daichi Shinigawa is a typical delinquent who wants nothing to do with high school. However, bespectacled Hana Adachi, the class representative, will do anything in her power to make sure Daichi participates in whatever events the school has to offer. If she has to surprise him in the boy's bathroom to get him to go on the school field trip, so be it! Daichi is confused as to why a class rep would care so much about a troublemaker like him; what could be the reason behind her actions?
Both mangas are stories focusing on a high school girl, who is a genius when it comes to fighting (or a genius in every area in Medaka Box case). That person have an important job (class president in Yankee-kun, and Student council president in Medaka Box ) and strong sense of duty. Her goal is to help people, and for that she will drag her poor male companion through hell. As the story progresses more characters gather around the strong heroine, and help achieve her goals.
Both stories are a mix of comedy, battles and a bit of romance. Boh makes you feel sorry for the guy, abused by the selfish girl.You should have a fun time reading either of them.
YtM and Medaka Box (during the first 16 chapters) have similar plot and similar characters. Namely they have an energetic girl leading a high school student council. Unlike YtM, Medaka Box contains some ecchi. Still, if you liked one of those manga you should give the other one a try.
President of the Student Council at the almost-all-boys Seika High School, the hard-as-nails Misaki Ayuzawa works every day to make life easier on the small population of co-eds who have enrolled there. Though an unholy terror to all things male during school hours, in order to provide for her impoverished family, she secretly works after school at a maid cafe in Akihabara. However, when campus hottie Usui Takumi wanders into the restaurant during her shift, suddenly she finds her reputation in school at his mercy...
If you like Medaka Box setting, namely the part about a**-kicking girl being president of a student council, then you should give Maid-sama! a try. It should be noted that both of those manga have some really crazy stuff going on. Also if you felt disappointed that the school life part in Medaka Box was dropped after just a handful of chapters, you might find it interesting that school life is present through most of Maid-sama!
The female leads in both series are quite similar. Both are insanely strong, very confident and somewhat open minded. The fact that one is rather smart while the other is not doesn't affect the similarity as much as one would expect. There many other similarities between those two and even the plot contains some similar themes. Anyway, if you liked the female lead in one series, you'll probably going to like the female lead in the other one (and maybe even the series itself).
Both are mangas in which selfish, arrogant and talented female lead tries to change the world in some way. Her methods are weird, her actions are bizarre but the outcome is usually good. There is also a poor male character, who have a crush on the heroine. He is constantly getting abused and dragged around at girl's pace in order to help with the peculiar plans. Also on a course of story a lot of other weird characters gather around the girl, and aid her in her actions.
Both are mainly comedy, with some romance mixed in (and battles in Medaka case). If you like the treatment Kyon is getting from Haruhi, you will also like Medaka+ Hitoyoshi combi)
On a side note - Haruhi have anime way better than the manga, so if you decided to check Haruhi after reading Medaka you might consider watching the anime instead ( 2006, not 2009 though. 2009 is an abomination due to "Endless 8")